<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
    <script src="../js/react.development.js"></script>
    <script src="../js/react-dom.development.js"></script>
    <script src="../js/babel.min.js"></script>
  </head>
  <body>
    <div id="test"></div>

    <script type="text/babel">
      class Demo extends React.Component {
        state = {
          elOpa: 1,
        };
        render() {
          return (
            <div>
              <h2
                style={{ opacity: this.state.elOpa }}
                ref={(el) => (this.hdEl = el)}
              >
                react
              </h2>
              <button onClick={this.removeHeader}>消失了</button>
            </div>
          );
        }

        removeHeader = () => {
          ReactDOM.unmountComponentAtNode(document.getElementById("test"));
        };

        componentDidMount() {
          this.timer = setInterval(() => {
            let { elOpa } = this.state;
            elOpa -= 0.1;
            if (elOpa <= 0) {
              elOpa = 1;
            }
            console.log(1);
            this.setState({
              elOpa,
            });
          }, 100);
        }

        componentWillUnmount() {
          clearInterval(this.timer);
        }
      }

      ReactDOM.render(<Demo />, document.getElementById("test"));
    </script>
  </body>
</html>
